Various methods of manufacturing contact lenses exist, for example, by lathing a lens from a disk (or button) of lens material. Typically, the button is mounted in a lathe collet and a back surface (corneal contacting) radius is formed. Subsequently, the button is then mounted by various means on a rounded end of a lens fixture, the rounded end having a curvature generally corresponding to that of the back surface radius of the button so that the front surface of the lens may be shaped. Additionally, various intermediate lathing operations, for example, cutting an edge chamfer in the button, cutting the lens to a desired thickness, and/or polishing the lens may also be performed.
In order to hold the button in place, typically, a single layer of adhesive (e.g., pitch, wax or the like) is applied or melted on the button and the button is placed on the tool. The adhesive hardens and secures the button to the tool. Generally speaking, the bond between the tool and the button must be strong enough to hold the button in place during manufacturing (e.g., lathing). Additionally, the adhesive must be strong enough that it will not flex under pressures exerted during the manufacturing operation performed on the button. However, notwithstanding the need to be strong to hold and resist flexure, it is desirable that the adhesive be removable, leaving a clean and undamaged lens surface.
Adhesive removal is accomplished by numerous means. For example, pitch removal is accomplished by physical removal (e.g., prying the pitch off, sonically dislodging it, etc.), cryogenic removal (freezing the pitch off), dissolving the pitch and/or melting the pitch. However, as newer lens materials have developed, the requirements for manufacturing the lenses have changed. For example, often, newer lens materials are softer, more flexible, more temperature sensitive, more sensitive to solvents and mechanical stress. Thus, traditional methods of removal of adhesive may suffer from various disadvantages.
For example, dissolving the adhesive with a solvent may damage the lens material. Additionally, with many of the known removal methods, time and temperature exposure to solvents must be precisely controlled, decreasing efficiencies and increasing manufacturing costs.
Water soluble waxes are desirable for use as an adhesive as the wax readily dissolves in a water bath, the water generally having few, if any, effects on the lens. Additionally, any remaining wax residues tend be readily removed with standard lens cleaners (e.g., those used by consumers). However, because water soluble waxes are softer and more flexible than traditional, non-soluble waxes and adhesives, the water soluble waxes generally cannot withstand the forces involved in lens manufacturing operations, particularly, high speed lathing operations.
Accordingly, a means for attaching a lens button to a lens fixture for manufacturing of contact lenses is desirable.